This invention relates to a device for adjusting the flow rate of air or air-fuel-mixture drawn into an internal combustion engine during idling.
Internal combustion engines usually have an auxiliary air passage which is connected to a main air passage in such a manner as to bypass an engine throttle valve. The auxiliary passage permits air to be drawn into the engine when the throttle valve is closed. A screw is located in the auxiliary passage to adjust the effective cross-sectional area thereof to determine the flow rate of air drawn into the engine during idling.
The engines usually have positive crankcase ventilation (PCV) and exhaust gas recirculation (EGR) systems for the purpose of emission control. These systems inevitably discharge contaminants, such as oil or carbon particles, into fresh air in the air passages. In addition, some dirt will inevitably pass an air filter or cleaner and will be entrained in the air flowing through the air passages.
When dirt or other contaminants accumulate on the idle-adjusting screw, the effective cross-sectional area of the auxiliary passage decreases from the desired value, reducing the flow rate of air drawn into the engine during idling. This causes a reduction in the engine rotational speed during idling.
Accordingly, some idle-adjusting devices are arranged to prevent dirt or other contaminants from adhering thereto and accumulating thereon, thereby keeping engine idle speed at an optimal level.